1. Technical Field
The present invention relates to a circuit and method for detecting leakage mainly of a charging/discharging circuit of a rechargeable battery, and particularly to a circuit and method for detecting leakage of a power supply device that drives motor for running an electric vehicle, such as hybrid car and electric car, for example.
2. Description of Related Art
High voltage is required to increase the output of a power supply device for running an electric vehicle. The reason is that output is proportional to the product of voltage and current. For example, the output voltage of a power supply device for running a hybrid car or an electric car is very high voltage of 200 V or more. Since, in a high-voltage power supply device, leakage causes a serious adverse effect, the device is not connected to a ground in consideration of safety. In order to prevent leakage, it is necessary for the power supply device that is not connected to a ground to detect a leakage resistance. The leakage resistance is a resistance between the power supply device and a ground. FIG. 4 corresponds to FIG. 1 in Japanese Patent Laid-Open Publication TOKUKAI No. 2003-169401, and shows a detection circuit for detecting the leakage resistance of a power supply device. A leakage detection circuit 50 shown in this Figure has a leakage detection resistance 51, a leakage detection switch 52, and a voltage detection circuit 53 that detects the voltage produced in the leakage detection resistance 51. When a leakage resistance Rr exists, in the state the leakage detection switch 52 is ON, a current flows in the leakage detection resistance 51. Accordingly, the voltage of the leakage detection resistance 51 is detected, thus, leakage can be detected.
However, it is difficult for this type of conventional leakage detection circuit to accurately calculate the leakage resistance value.